A recent driving and traffic simulation study from the University of Minnesota suggests several cost-effective ways to address rural highway safety at the intersection
The rural road safety crisis is invisible to many Americans. Only about 20 percent of the US population lives in rural areas, and only about one-third of all miles driven in the US is driven on rural highways. Nonetheless, rural Americans account for half of all traffic fatalities. Minnesota is no exception: from 2008 to 2012, nearly 42 percent of severe crashes at Minnesota intersections resulted in serious injuries and fatalities, with the most severe accidents occurring at rural intersections.
According to Tracey von Bargen, county engineer for Grant County, Minnesota, “We’ve known that sight distances were factors in rural intersection crashes. This study gave us the hard data showing how long sight distances should actually be to allow drivers sufficient time and space at rural thru-stop intersections.”
Traffic Simulation for Rural Driver Safety
In 2019 Nichole Morris and her team set out to determine the optimal sight distances for rural four-way intersections. They worked at the University of Minnesota Department of Mechanical Engineering’s HumanFIRST lab, a facility outfitted with a full cab immersive passenger vehicle simulator from RealTime Technologies. This simulator was built on a 2013 Ford Fusion chassis with realistic controls and the latest generation of traffic simulation software and projection hardware—key features for this study.
Morris and her team developed ten simulation scenarios to run on the RTI sim. All were modeled on existing Minnesota rural intersections and roadways in consultation with state, county, and research engineers familiar with those areas.
The first nine scenarios were designed to explore how drivers determine when it’s safe to proceed through an intersection when driving along a minor rural road that crosses a faster “main line” road. The driver needed to judge when it was safe to proceed through the intersection under different driving/visibility conditions. These varying conditions included varying sight distance, oncoming vehicle speed, and traffic gaps from 3 to 12 seconds between vehicles.
Morris and her team also developed an extended 19-mile drive, where the study participant was piloting their vehicle along the main line road. In these trials, the participant was presented with 18 separate “thru-stops,” where minor legs intersected with the mainline. Different thru-stop intersections along the drive offered different sight distances and the simulated drivers traveling those minor roads behaved differently: some stopped at the intersection’s painted stop bar, others stayed farther back, nosed out, or crept into the intersection.
Traffic Simulation Findings: Inexpensive Changes Can Reduce Driver Stress
Morris’ team concluded that, for both drivers traveling the main line road and those crossing via a minor road, common 400- and 600-foot sight distances were too short—especially at the speeds commonly traveled on rural highways (i.e., faster than 55 miles per hour). These shorter sight distances were also the most stressful conditions for participants.
Having 1,000 feet of sight distance allowed both drivers on the mainline and the minor legs to negotiate intersections more safely and more confidently. Additionally, they found that drivers on the faster mainline road naturally slowed more when cars at minor intersections were stopped closer to the intersection itself. This points to an extremely inexpensive “double win”:
By moving the painted stop bar on minor roads closer to the intersection, the driver on the minor road gets a longer sight distance (reducing their stress and increasing safety), while the driver on the mainline has an easier time seeing potential hazards—”an inexpensive change,” Morris’ team noted, “with potentially significant benefits.”